The controls I have in mind for my merephone project: 2 buttons & a joystick-switch for primary input; & a 4-gray epaper display for primary output.
My initial thoughts were *slightly* different, before I got my hands on actual hardware.
Its obvious how I'd use this for menus (be it of notifications, contacts, texts, files/folders, dates & times, settings, etc) with back & add buttons. But I also reckon great typing's vital for a modern featurephone!
1/3?
An "8pen" idea I've heard of for typing is to have you draw loops starting & ending in a center position. The 1st & final side the loop is on can both give 2bits of scancode, clockwise vs anti-clockwise gives another bit. Yielding 5bit scancodes.
Using the buttons as a shift key gives a 6th bit yielding 64 keys. And there's a few gestures left over that can be used to edit text, accept/reject the text, or navigate between keyboards.
I'd have a notation for communicating the layout onscreen.
2/